Hydronic Heating Flow Calculator
Water flow a heating circuit needs to deliver its kW at the chosen ΔT.
Heat pumps need 2–3× boiler-era flow for the same kW (smaller ΔT) — check old pipework before swapping the heat source.
Formula
Hydronic Heating Flow Calculator is a free hydronic flow rate for HVAC designers, technicians and energy auditors — instant, accurate and 100% client-side, with the governing formula and reference shown next to the result so the number can be defended, not just quoted.
About Hydronic Heating Flow Calculator
Water flow a heating circuit needs to deliver its kW at the chosen ΔT. The calculation implements ṁ = Q / (c_p·ΔT) (CIBSE Guide B — hydronic distribution). Heat pumps need 2–3× boiler-era flow for the same kW (smaller ΔT) — check old pipework before swapping the heat source.
How to use Hydronic Heating Flow Calculator
- 1Enter Heat to deliver in kW.
- 2Enter Design ΔT (flow − return) in °C (Boilers 11–20 · heat pumps 5–8).
- 3Read Flow rate, Flow rate instantly — no submit button needed.
- 4Need US units? Flip the SI/Imperial toggle and every field converts.
Why use Hydronic Heating Flow Calculator?
- ✓Implements the standard formula — ṁ = Q / (c_p·ΔT)
- ✓Reference cited on-page: CIBSE Guide B — hydronic distribution
- ✓One-click SI ⇄ Imperial toggle — values convert in place, physics stays in SI
- ✓Live worked example: the substitution recomputes from your numbers
- ✓Runs entirely in your browser — nothing uploaded, free forever
Frequently asked questions
What formula does the Hydronic Heating Flow Calculator use?+
It computes ṁ = Q / (c_p·ΔT), per CIBSE Guide B — hydronic distribution. The formula is displayed under the result along with a worked example substituted with your own inputs.
What should I keep in mind when using this calculator?+
Heat pumps need 2–3× boiler-era flow for the same kW (smaller ΔT) — check old pipework before swapping the heat source.
Is this based on ASHRAE methods?+
The calculations follow the standard ASHRAE/ISHRAE formulations cited under the result, simplified where industry practice does the same. For permit-grade design, confirm with the full code procedure.
Is the Hydronic Heating Flow Calculator free to use?+
Yes — completely free, no sign-up, no limits. It runs client-side in your browser, so inputs stay private and results are instant even on slow connections.
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